You're the dealer's best friend: you trust them and pay what they ask
unquestioningly, even if, as can be attested by members of this group,
your life may be endangered by their carelessness.

Quis custodiet ipsos custodes?

You don't.

I will.
blurp

"In the absence of facts I will speculate wildly."

You're missing one important part of the pleasure of automobile
maintenance -- that of doing it yourself.

The majority of people who use this forum believe that a my-hands-on
approach to maintenance is useful and a pleasure, as well as saving
money. I hire a professional when something is beyond my skills or is
cost-effective (my time and my money). Applies to my car, my house, my
garden, my hobby.

Some go a lot farther than I would in what you can do yourself and
what needs to go to the shop.  In fact, my last repair job at the shop
included the offer of a lesson on how to do radiator flushes myself
(radiator/intercooler leak).

When I go in to the shop, I already know what needs to be done, saving
them time and effort in diagniosing problems by eliminating the
obvious. I invariable get a quick lesson from a mechanic on what I'd
missed or on some other aspect of maintaining the car.

My local mechanic believes that a knowledgable customer is an
investment of his time. The less time that he fa*ts around trying to
figure out what a customer says is a problem means that he has that
much more time to work on a real problem.

BTW, non carborundum illegitimi is a valid phrase -- A quick search
reveals that its used by a SAC bomber squadron as well as the UASF
Test Pilot School.

http://www.edwards.af.mil/history/docs_html/center/test_pilot_school.html